[Pigments and Binders]
Malachite, one of the first green pigments, was first
used in Egypt and China. In fact, Egyptians probably used the pigment as
eye paint even before the first Egyptian dynasty. It is found on tomb paintings
from the Fourth Dynasty on. In Western China, malachite is found in many
paintings from the ninth and tenth centuries. Europeans did not use malachite
very much in medieval times, but it was very popular during the Renaissance.
However, it had been replaced by synthetic green pigments by about 1800.
On the other hand, Japanese painters used the pigment even in this century
on screen paintings. In the West, it has now lost most practical importance
and is not usually found on the market.
Malachite's formula is CuCO3.Cu(OH)2; it is poisonous. It forms fairly permanent paints and is unaffected by strong light. When it is slowly heated, finely crushed malachite gives off water and carbon dioxide (CO2), finally becoming black cupric oxide (CuO). In acid solution, it dissolves and releases carbon dioxide, but remains green. In reaction with hot sodium hydroxide (NaOH), cupric oxide forms on the surface, but the pigment does not react with cold sodium hydroxide. Finely powdered malachite is also slowly darkened by hydrogen sulfide (H2S). The picture to the right shows malachite particles in mounting medium, magnified 20 times. The film was exposed to light for one fourth of a second with the condenser stage set at .15 and the light set at 6.
Preparation and Artistic Use
Malachite occurs naturally as a semiprecious stone, which is frequently
cut and polished into gemstones and figurines.
It usually occurs in association with azurite, a blue stone. Large deposits
are found in the Ural Mountains of the former U.S.S.R. and in Zaire, Zimbabwe,
and Chile. The stone is usually found in large masses banded with shades
of green ranging from pale green to almost black. To prepare the pigment,
this stone is crushed and ground into a fine, chalk-like powder, which
is then washed and levigated--swirled in water to separate the finer particles.
The powder becomes paler the more it is ground. For instance, Japanese
painters used coarsely ground malachite for the deep green of foliage and
used the finely ground pigment for the brighter greens of clothing (Ashok). When used as a paint, malachite's shade also changes
with the medium used. As a watercolor, it is a pale green, but it becomes
darker in oil. It works better in egg tempera than in oil.
My Lab Results
(right) Malachite in oil binder; x20 magnification; lighting at 6; condenser at .25; .5 second exposure.
In the lab, finely-ground (and thus pale green) malachite was made into three different kinds of paint: an oil paint using linseed oil, a paint in egg tempera, and a watercolor using gum arabic binder. The pigment did not seem to mix with any one binder better or worse than with the others, although the egg tempera dried too quickly to be tested very well. The watercolor was a pale powder green, slightly darker than the plain pigment, while the oil paint was darker and the egg paint's shade was between those of the other two and had a more yellowish hue. When malachite paint was mixed with red and yellow ones such as vermillion and yellow ochre, various shades of brown resulted. Malachite made ultramarine become a paler shade of blue and was made paler by calcium carbonate.
When tested with the colorimeter, a sample of malachite watercolor paint had a Lightness coordinate of 77, an a coordinate of -25, and a b coordinate of +5. The L coordinate shows that the paint was fairly bright, as 100 is the highest possible. The a coordinate shows that the paint was more green than red while the low b coordinate shows that it was slightly more yellow than blue. When viewed under the microscope, the pigment, with and without binder, had green-colored crystals of varying sizes. Here are more pictures of the microscope slides.
(right) Malachite in gum arabic binder; x20 magnification; lighting at 6; condenser at .3; .25 second exposure.
(right) Malachite in egg tempera; x20 magnification; lighting at 6;
condenser .15; 1 second exposure.
Joy Reeves, 1997.